Off-road motorcycles are designed for recreational riding and competition racing over natural terrain and man-made courses. Motorcross and Enduro are the two best know types of competition. Many manufacturers make these types of motorcycles, most notably Yamaha, BMW, Suzuki etc.
These off road motorcycles work in a very harsh environment and have many moving parts that are often covered with mud. Mud is essentially a fluid mixture of fine dirt and water. The dirt particles within the mud can vary from coarse sand, to very fine clay. The suspension components of, the motorcycle are the parts that suffer worst from constant exposure to this abrasive mix. These suspension components are attached to the wheels, (so are very exposed and close to the ground), and must travel through long distances to keep the wheels in contact with the terrain.
While it is possible to keep that mud out of many of the moving suspension pivots with conventional seals, the front forks of off road motorcycles are very difficult to protect. All off road motorcycles use telescopic sliding forks. These forks consist of one telescopic leg on each side of the front wheel. The internals of these telescopic legs are very complex and are filled with a myriad of valves, springs, and damping oil.
Almost all forks currently in production are commonly called USD, (short for Upside Down) forks. This is because the very first, (traditional), telescopic motorcycle forks used an inner tube rigidly mounted to the motorcycle, with the outer tube attached to the wheel. This kept the sliding portion of the fork high up on the motorcycle, and allowed a concertina style boot to be used over the exposed leg for protection. In recent years, however, all off-road motorcycle forks have been turned upside down. The larger diameter outside tubes are now clamped rigidly to the motorcycle steering frame, and the smaller diameter inner tubes are now attached to the wheel. This has been done primarily to increase the rigidity of the assembly. While there is a benefit in rigidity, the unfortunate consequence is that the exposed sliding portion of the leg is now below the fender of the motorcycle, very close to the front wheel. It is now in a position where it is very exposed to damage and mud, and is difficult to protect.
Additionally, as fork tube diameters have been increased in pursuit of increased rigidity, fork seal pressure against the leg has been reduced so as not to restrict fork movement.
The seals that stop mud and dirt entering the telescopic legs are fairly conventional oil seals. Two seals are used, an outer dust seal, and an inner oil seal. Because the free and rapid movement of the telescoping parts is vital for effective suspension control, it is critical that these seals are not so tight as to restrict the sliding is action. The obvious problem is that the looser the seal is on the sliding inner tuba, the less likely it is to keep dirt and water out of the easily damaged internals. The larger the fork inner tube diameter, the worse the compromise.
While it is theoretically possible to still cover the outside of these Upside Down telescoping forks with a ‘concertina’ style over-boot, these protective covers introduce, other problems. Although they have been used on some brands of motorcycle at some times, they are generally considered an unacceptable compromise. There are no production off-road motorcycles currently sold with this style of protectors.
In all cases, however, a rigid plastic stone shield is fixed in front of each fork leg, (normally at a distance of around 10 mm from the leg), to prevent hard objects contacting and damaging the critical sliding components. These stone guards do prevent some mud from contacting the legs, but they in turn make access to the legs for cleaning quite difficult. These stone guards are positioned away from the leg so that they do no not provide a place for mud to gather and abrade the leg.
The result is that in particular environments, fork seal life on off-road motorcycles is very limited. The situation is probably worst in hot muddy conditions where clay type mud quickly dries onto exposed sliding components. When this dried slurry is forced into the seal, often a small amount is pushed through the seal and inside the fork, tube. The first sign of ineffective seals is internal fork lubricating oil becoming visible around the seal area. If not addressed quickly, this oil will run down the fork tube and onto the brakes with dangerous consequences.
Very frequently, the initial leakage is associated with seals that are not actually damaged at that point, but are being prevented from sealing effectively due to the ingress of dirt and other debris. Removing this foreign material immediately allows the seal to work effectively again. If the abrasive contaminating material is left there, the seals and or suspension components are quickly damaged. Additionally, it is well known that the removal of any contaminants before a seal actually starts to leak will significantly extend the seal life.
Conventionally, the forks must be completely disassembled to allow access to the seals. This is an expensive and time consuming process that must be carried out in a well equipped workshop and requires significant technical expertise. It is known, however, that by prising the dust seal away, a thin piece of plastic sheet can sometimes be forced inside the oil seal to remove at least some of the dirt without disassembling the fork tube. This is seen more as an ‘emergency’ measure, rather than a mechanically sound way of removing the contaminants.
Unfortunately, because the outside of the fork tube is protected by the rigid plastic stone shield, this shield must be removed before the plastic can be run completely around the seal. As a result, this is rarely carried out as a preventative measure. Additionally, there is often not time to remove the stone guard when the oil is first noticed, and the motorcycle is ridden, (with subsequent damage). Even with the stone guards removed, it is difficult to run a piece of plastic sheet evenly around the seal. Available in the market are specially shaped plastic strips, as disclosed in published US patent application 2004/0117932 A1, and sold in motorcycle shops explicitly for this purpose, but these are little better than a piece of cut-up credit card or the like. The strip is illustrated in FIG. 1 of the drawings.
It is, an object of the present invention to address or at least ameliorate some of the above disadvantages.
The present invention comprises a tool that allows fork seals to be thoroughly cleaned very quickly without the removal of any protective guarding or disassembly of the fork leg.
Notes
    1. The term “comprising” (and grammatical variations thereof) is used in this specification in the inclusive sense of “having” or “including”, and not in the exclusive sense of “consisting only of”.    2. The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.